There are a number of devices available for the delivery of breathable gas, including air, to a patient for the treatment of disordered breathing, in particular, sleep disordered breathing. For example, in the treatment of sleep apnea, including obstructive sleep apnea, air is often delivered at continuous positive air pressure (CPAP) wherein air is supplied continuously at a pressure greater than ambient to the airway of a sleeping patient through a mask to keep the patient's airway open for effective respiration.
It is important for continuous therapeutic benefit from pressurised air for the air and other gases to be delivered at a pressure and a flow rate appropriate for the desired breathing pattern. The delivery of gas should not induce the feeling of “blowing into the wind” during treatment. It is known in the art that a system including a gas delivery device, often with gases humidified for comfort, incorporates various combinations of fans, air conduits, face masks, and mask assemblies. Gas-delivery devices may be controlled by circuitry and computer software to deliver the gas through an air conduit to a face mask at a desired flow rate and pressure.
Prior art gas-delivery systems, methods, and devices generally include a limited number of desirable features. For example, gas may be delivered at only one or a limited number of flow rates. Similarly, gas may be delivered simply as pressurised air, the unhumidified pressurised air having the potential to cause discomfort by drying out the breathing passages of a patient using the gas for treatment. A device delivering gases may be large and cumbersome to manipulate. It is known in the art that fans used in devices can be noisy and cause disturbance to the sleep of patients using the devices. Prior art devices are known wherein flow rate is controlled by changes in motor speed. Such devices are limited in efficacy of controlling flow rate by the speed with which pressure change can be effected by the dynamics of the motor.
What is needed is a gas-delivery system and methods for delivering gases that include devices that are relatively easy to manipulate, operate, quiet, and deliver gases with appropriate humidification at desired flow rates and pressures. Further, a gas-delivery system should be relatively easy to manufacture and to transport. A gas-delivery system should be able switch between pressure levels quickly to accommodate expiratory and breath changes.
A reference herein to a gas-delivery system includes systems, and devices for CPAP, VPAP (Variable Positive Air Pressure), BiPAP (Bi-Level Positive Air Pressure), or APAP (Automatic Positive Air Pressure), all of which describe the flow rate and pressure of gases delivered by a device or a system. For example, BiPAP switches to a lower airflow when appropriate during expiration by a patient so that the patient has more comfortable breathing by not having to breathe into a “force of air”. Further acronyms used to describe elements in this document are provided with their meanings in Table I. In this document a reference to “comprising” is a reference to “including”, where both words are used in a context that is not limiting.